观书散遗帙,探古穷至妙。这篇文章主要讲述Android RxJava使用介绍 RxJava的操作符相关的知识,希望能为你提供帮助。
本篇文章继续介绍下面类型的操作符
- Combining Observables(Observable的组合操作符)
- Error Handling Operators(Observable的错误处理操作符)
combineLatest操作符把两个Observable产生的结果进行合并,合并的结果组成一个新的Observable。
这两个Observable中随意一个Observable产生的结果,都和还有一个Observable最后产生的结果,依照一定的规则进行合并。
流程图例如以下:
文章图片
调用样例例如以下:
//产生0,5,10,15,20数列
Observable<
Long>
observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(5);
//产生0,10,20,30,40数列
Observable<
Long>
observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
Observable.combineLatest(observable1, observable2, new Func2<
Long, Long, Long>
() {
@Override
public Long call(Long aLong, Long aLong2) {
return aLong+aLong2;
}
}).subscribe(new Subscriber<
Long>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Long aLong) {
System.out.println("Next: " + aLong);
}
});
执行结果例如以下:
Next: 0
Next: 5
Next: 15
Next: 20
Next: 30
Next: 35
Next: 45
Next: 50
Next: 60
Sequence complete.
join操作符
join操作符把相似于combineLatest操作符,也是两个Observable产生的结果进行合并,合并的结果组成一个新的Observable。可是join操作符能够控制每一个Observable产生结果的生命周期,在每一个结果的生命周期内,能够与还有一个Observable产生的结果依照一定的规则进行合并。流程图例如以下:
文章图片
join方法的使用方法例如以下:
observableA.join(observableB,
observableA产生结果生命周期控制函数,
observableB产生结果生命周期控制函数。
observableA产生的结果与observableB产生的结果的合并规则)
调用样例例如以下:
//产生0,5,10,15,20数列
Observable<
Long>
observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(5);
//产生0,10,20,30,40数列
Observable<
Long>
observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
observable1.join(observable2, new Func1<
Long, Observable<
Long>
>
() {
@Override
public Observable<
Long>
call(Long aLong) {
//使Observable延迟600毫秒执行
return Observable.just(aLong).delay(600, TimeUnit.MILLISECONDS);
}
}, new Func1<
Long, Observable<
Long>
>
() {
@Override
public Observable<
Long>
call(Long aLong) {
//使Observable延迟600毫秒执行
return Observable.just(aLong).delay(600, TimeUnit.MILLISECONDS);
}
}, new Func2<
Long, Long, Long>
() {
@Override
public Long call(Long aLong, Long aLong2) {
return aLong + aLong2;
}
}).subscribe(new Subscriber<
Long>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Long aLong) {
System.out.println("Next: " + aLong);
}
});
执行结果例如以下:
Next: 0
Next: 5
Next: 15
Next: 20
Next: 30
Next: 35
Next: 45
Next: 50
Next: 60
Sequence complete.
groupJoin操作符
groupJoin操作符很相似于join操作符,差别在于join操作符中第四个參数的传入函数不一致。其流程图例如以下:
文章图片
【Android RxJava使用介绍 RxJava的操作符】调用样例例如以下:
//产生0,5,10,15,20数列
Observable<
Long>
observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(5);
//产生0,10,20,30,40数列
Observable<
Long>
observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
observable1.groupJoin(observable2, new Func1<
Long, Observable<
Long>
>
() {
@Override
public Observable<
Long>
call(Long aLong) {
return Observable.just(aLong).delay(1600, TimeUnit.MILLISECONDS);
}
}, new Func1<
Long, Observable<
Long>
>
() {
@Override
public Observable<
Long>
call(Long aLong) {
return Observable.just(aLong).delay(600, TimeUnit.MILLISECONDS);
}
}, new Func2<
Long, Observable<
Long>
, Observable<
Long>
>
() {
@Override
public Observable<
Long>
call(Long aLong, Observable<
Long>
observable) {
return observable.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong2) {
return aLong + aLong2;
}
});
}
}).subscribe(new Subscriber<
Observable<
Long>
>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Observable<
Long>
observable) {
observable.subscribe(new Subscriber<
Long>
() {
@Override
public void onCompleted() {}@Override
public void onError(Throwable e) {}@Override
public void onNext(Long aLong) {
System.out.println("Next: " + aLong);
}
});
}
});
执行结果例如以下:
Next: 0
Next: 5
Next: 10
Next: 15
Next: 20
Next: 25
Next: 30
Next: 35
Next: 40
Next: 45
Next: 50
Next: 60
Next: 55
Sequence complete.
merge操作符
merge操作符是依照两个Observable提交结果的时间顺序,对Observable进行合并,如ObservableA每隔500毫秒产生数据为0,5,10,15,20。而ObservableB每隔500毫秒产生数据0,10,20,30,40。当中第一个数据延迟500毫秒产生,最后合并结果为:0,0,5,10,10,20,15,30,20,40; 其流程图例如以下:
文章图片
调用样例例如以下:
//产生0,5,10,15,20数列
Observable<
Long>
observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(5);
//产生0,10,20,30,40数列
Observable<
Long>
observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
Observable.merge(observable1, observable2)
.subscribe(new Subscriber<
Long>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Long aLong) {
System.out.println("Next:" + aLong);
}
});
执行结果例如以下:
Next:0
Next:0
Next:5
Next:10
Next:10
Next:20
Next:15
Next:30
Next:20
Next:40
Sequence complete.
mergeDelayError操作符
从merge操作符的流程图能够看出,一旦合并的某一个Observable中出现错误,就会立即停止合并,并对订阅者回调执行onError方法,而mergeDelayError操作符会把错误放到全部结果都合并完毕之后才执行,其流程图例如以下:
文章图片
调用样例例如以下:
//产生0,5,10数列,最后会产生一个错误
Observable<
Long>
errorObservable = Observable.error(new Exception("this is end!"));
Observable <
Long >
observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(3).mergeWith(errorObservable.delay(3500, TimeUnit.MILLISECONDS));
//产生0,10,20,30,40数列
Observable<
Long>
observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
Observable.mergeDelayError(observable1, observable2)
.subscribe(new Subscriber<
Long>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Long aLong) {
System.out.println("Next:" + aLong);
}
});
执行结果例如以下:
Next:0
Next:0
Next:5
Next:10
Next:10
Next:20
Next:30
Next:40
Error: this is end!
startWith操作符
startWith操作符是在源Observable提交结果之前。插入指定的某些数据。其流程图例如以下:
文章图片
调用样例例如以下:
Observable.just(10,20,30).startWith(2, 3, 4).subscribe(new Subscriber<
Integer>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
执行结果例如以下:
Next:2
Next:3
Next:4
Next:10
Next:20
Next:30
Sequence complete.
switchOnNext操作符
switchOnNext操作符是把一组Observable转换成一个Observable,转换规则为:对于这组Observable中的每一个Observable所产生的结果,假设在同一个时间内存在两个或多个Observable提交的结果,仅仅取最后一个Observable提交的结果给订阅者,其流程图例如以下:
文章图片
调用样例例如以下:
//每隔500毫秒产生一个observable
Observable<
Observable<
Long>
>
observable = Observable.timer(0, 500, TimeUnit.MILLISECONDS).map(new Func1<
Long, Observable<
Long>
>
() {
@Override
public Observable<
Long>
call(Long aLong) {
//每隔200毫秒产生一组数据(0,10,20,30,40)
return Observable.timer(0, 200, TimeUnit.MILLISECONDS).map(new Func1<
Long, Long>
() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
}
}).take(2);
Observable.switchOnNext(observable).subscribe(new Subscriber<
Long>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Long aLong) {
System.out.println("Next:" + aLong);
}
});
执行结果例如以下:
Next:0
Next:10
Next:20
Next:0
Next:10
Next:20
Next:30
Next:40
Sequence complete.
zip操作符
zip操作符是把两个observable提交的结果,严格依照顺序进行合并,其流程图例如以下:
文章图片
调用样例例如以下:
Observable<
Integer>
observable1 = Observable.just(10,20,30);
Observable<
Integer>
observable2 = Observable.just(4, 8, 12, 16);
Observable.zip(observable1, observable2, new Func2<
Integer, Integer, Integer>
() {
@Override
public Integer call(Integer integer, Integer integer2) {
return integer + integer2;
}
}).subscribe(new Subscriber<
Integer>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
执行结果例如以下:
Next:14
Next:28
Next:42
Sequence complete.
Error Handling Operators(Observable的错误处理操作符)onErrorReturn操作符
onErrorReturn操作符是在Observable错误发生或异常的时候(即将回调oError方法时),拦截错误并执行指定的逻辑,返回一个跟源Observable同样类型的结果。最后回调订阅者的onComplete方法。其流程图例如以下:
文章图片
调用样例例如以下:
Observable<
Integer>
observable = Observable.create(new Observable.OnSubscribe<
Integer>
() {
@Override
public void call(Subscriber<
? super Integer>
subscriber) {
if (subscriber.isUnsubscribed()) return;
//循环输出数字
try {
for (int i = 0;
i <
10;
i++) {
if (i == 4) {
throw new Exception("this is number 4 error!
");
}
subscriber.onNext(i);
}
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
}
});
observable.onErrorReturn(new Func1<
Throwable, Integer>
() {
@Override
public Integer call(Throwable throwable) {
return 1004;
}
}).subscribe(new Subscriber<
Integer>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
执行结果例如以下:
Next:0
Next:1
Next:2
Next:3
Next:1004
Sequence complete.
onErrorResumeNext操作符
onErrorResumeNext操作符跟onErrorReturn相似,仅仅只是onErrorReturn仅仅能在错误或异常发生时仅仅返回一个和源Observable同样类型的结果,而onErrorResumeNext操作符是在错误或异常发生时返回一个Observable,也就是说能够返回多个和源Observable同样类型的结果,其流程图例如以下:
文章图片
调用样例例如以下:
Observable<
Integer>
observable = Observable.create(new Observable.OnSubscribe<
Integer>
() {
@Override
public void call(Subscriber<
?
super Integer>
subscriber) {
if (subscriber.isUnsubscribed()) return;
//循环输出数字
try {
for (int i = 0;
i <
10;
i++) {
if (i == 4) {
throw new Exception("this is number 4 error。");
}
subscriber.onNext(i);
}
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
}
});
observable.onErrorResumeNext(new Func1<
Throwable, Observable<
? extends Integer>
>
() {
@Override
public Observable<
? extends Integer>
call(Throwable throwable) {
return Observable.just(100,101, 102);
}
}).subscribe(new Subscriber<
Integer>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
执行结果例如以下:
Next:0
Next:1
Next:2
Next:3
Next:100
Next:101
Next:102
Sequence complete.
onExceptionResumeNext操作符
onExceptionResumeNext操作符和onErrorResumeNext操作符相似。不同的地方在于onErrorResumeNext操作符是当Observable错误发生或异常时触发,而onExceptionResumeNext是当Observable发生异常时才触发。
这里要普及一个概念就是,java的异常分为错误(error)和异常(exception)两种。它们都是继承于Throwable类。
错误(error)通常是比較严重的系统问题,比方我们常常遇到的OutOfMemoryError、StackOverflowError等都是错误。错误一般继承于Error类,而Error类又继承于Throwable类,假设须要捕获错误,须要使用try..catch(Error e)或者try..catch(Throwable e)句式。
使用try..catch(Exception e)句式无法捕获错误
异常(Exception)也是继承于Throwable类。通常是依据实际处理业务抛出的异常。分为执行时异常(RuntimeException)和普通异常。普通异常直接继承于Exception类。假设方法内部没有通过try..catch句式进行处理。必须通过throws关键字把异常抛出外部进行处理(即checked异常);而执行时异常继承于RuntimeException类,假设方法内部没有通过try..catch句式进行处理,不须要显式通过throws关键字抛出外部。如IndexOutOfBoundsException、NullPointerException、ClassCastException等都是执行时异常。当然RuntimeException也是继承于Exception类,因此是能够通过try..catch(Exception e)句式进行捕获处理的。
onExceptionResumeNext流程图例如以下:
文章图片
调用样例例如以下:
Observable<
Integer>
observable = Observable.create(new Observable.OnSubscribe<
Integer>
() {
@Override
public void call(Subscriber<
?
super Integer>
subscriber) {
if (subscriber.isUnsubscribed()) return;
//循环输出数字
try {
for (int i = 0;
i <
10;
i++) {
if (i == 4) {
throw new Exception("this is number 4 error!");
}
subscriber.onNext(i);
}
subscriber.onCompleted();
} catch (Throwable e) {
subscriber.onError(e);
}
}
});
observable.onExceptionResumeNext(Observable.just(100, 101, 102)).subscribe(new Subscriber<
Integer>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
执行结果例如以下:
Next:0
Next:1
Next:2
Next:3
Next:100
Next:101
Next:102
Sequence complete.
retry操作符
retry操作符是当Observable错误发生或者异常时,又一次尝试执行Observable的逻辑。假设经过n次又一次尝试执行后仍然出现错误或者异常,则最后回调执行onError方法。当然假设源Observable没有错误或者异常出现,则依照正常流程执行。
其流程图例如以下:
文章图片
调用样例例如以下:
Observable<
Integer>
observable = Observable.create(new Observable.OnSubscribe<
Integer>
() {
@Override
public void call(Subscriber<
?
super Integer>
subscriber) {
if (subscriber.isUnsubscribed()) return;
//循环输出数字
try {
for (int i = 0;
i <
10;
i++) {
if (i == 4) {
throw new Exception("this is number 4 error!");
}
subscriber.onNext(i);
}
subscriber.onCompleted();
} catch (Throwable e) {
subscriber.onError(e);
}
}
});
observable.retry(2).subscribe(new Subscriber<
Integer>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
执行结果例如以下:
Next:0
Next:1
Next:2
Next:3
Next:0
Next:1
Next:2
Next:3
Next:0
Next:1
Next:2
Next:3
Error: this is number 4 error!
retryWhen操作符
retryWhen操作符相似于retry操作符,都是在源observable出现错误或者异常时,又一次尝试执行源observable的逻辑,不同在于retryWhen操作符是在源Observable出现错误或者异常时,通过回调第二个Observable来推断是否又一次尝试执行源Observable的逻辑。假设第二个Observable没有错误或者异常出现。则就会又一次尝试执行源Observable的逻辑,否则就会直接回调执行订阅者的onError方法。其流程图例如以下:
文章图片
调用样例例如以下:
Observable<
Integer>
observable = Observable.create(new Observable.OnSubscribe<
Integer>
() {
@Override
public void call(Subscriber<
? super Integer>
subscriber) {
System.out.println("subscribing");
subscriber.onError(new RuntimeException("always fails"));
}
});
observable.retryWhen(new Func1<
Observable<
? extends Throwable>
, Observable<
?>
>
() {
@Override
public Observable<
?>
call(Observable<
? extends Throwable>
observable) {
return observable.zipWith(Observable.range(1, 3), new Func2<
Throwable, Integer, Integer>
() {
@Override
public Integer call(Throwable throwable, Integer integer) {
return integer;
}
}).flatMap(new Func1<
Integer, Observable<
?
>
>
() {
@Override
public Observable<
?
>
call(Integer integer) {
System.out.println("delay retry by " + integer + " second(s)");
//每一秒中执行一次
return Observable.timer(integer, TimeUnit.SECONDS);
}
});
}
}).subscribe(new Subscriber<
Integer>
() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
执行结果例如以下:
subscribing
delay retry by 1 second(s)
subscribing
delay retry by 2 second(s)
subscribing
delay retry by 3 second(s)
subscribing
Sequence complete.
好了,先介绍这么多。下回继续介绍其它的操作符。敬请期待!
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